SMTP is the acronym for Simple Mail Transfer Protocol, which is as its name implies, is a protocol for sending email messages across the internet. This is used in conjunction with POP3 and IMAP which are also protocols that enable you to download messages from a mail server straight to your computer. Note that SMTP caters to outgoing emails while POP3 and IMAP are used for incoming mail.

Now, the standard port implemented for SMTP connections is Internet port 25. If you happen to be having trouble sending messages, chances are likely that your internet service provider is blocking this port. Hence, the reason why it’s recommended that you use an alternative SMTP.

Depending on your OS, here’s how to check whether or not your ISP is blocking port 25:

1. Check port 25 in Windows
Click on the Start menu button, which is located at the lower left corner of your screen. Look for the tab “Run” (Note that you can also press the Windows Key and the R key simultaneously to open the run prompt). Click on it and a new will pop up. In the text field of this window, type cmd then press the “Enter” key. Another window called the “MS-DOS prompt” or “command-prompt” will open. Type the following command in the command prompt window and press “Enter”:telnet my-domain-name.com 25

2. Check port 25 in Mac
A pre-installed terminal emulator is delivered for each Mac OS. Usually located under your Mac HD -> “Applications” directory -> Utilities sub-directory, the terminal is a tool which allows you to execute command from the command line. When the window opens, a command line with a flashing cursor on it will appear so you can immediately start typing. Type the following command in the command prompt window and press “Enter”:telnet my-domain-name.com 25

3. Check port 25 in Linux
In order to check the connection on port 25 to your website, open your favorite terminal emulator and execute the following command: telnet my-domain-name.com 25.

Author: Alex Burgess